Gas Compressor

ABSTRACT

A bearing oil feeding amount is appropriately controlled with respect to specifications of a discharge pressure (bearing load) and a rotation speed. A gas compressor has: a compressor main body that compresses gas and has a rotor; a bearing for supporting the rotor onto a compressor main body casing; an oil case that stores a lubricating oil to be supplied to the bearing; a lubricating oil pipe through which the lubricating oil is circulated from the oil case to the bearing; an oil pump that pumps the lubricating oil from the oil case to the bearing via the lubricating oil pipe; a flow amount control means for adjusting an amount of lubricating oil that circulates through the lubricating oil pipe; an electric motor that supplies power to the rotor; an inverter that outputs a rotation frequency of the electric motor; a pressure sensor that detects the discharge pressure of the compressor main body; and a control unit that determines a lubricating oil supply amount to the bearing on the basis of the load on the bearing corresponding to the pressure detected by the pressure sensor and the rotation speed of the rotor corresponding to the rotation frequency output by the inverter, and that controls the flow amount control means on the basis of the lubricating oil supply amount.

TECHNICAL FIELD

The present invention relates to a gas compressor, specifically to a gas compressor that controls the amount of oil supplied to a bearing according to the rotation speed and the discharge pressure.

BACKGROUND ART

Oil-free screw compressors that do not require a supply of oil or water to the compression working chamber are known. For example, screw compressors etc. that have a pair of male and female screw rotors rotatable in a non-contact, oil-free state and that compress gas, such as air, with these screw rotors are known. An oil-free screw compressor is generally configured to include lubricating oil for lubricating and cooling the rotor bearing, the gear, the compressor main body, etc., and a heat exchanger that exchanges heat with the lubricating oil, and to circulate the lubricating oil by an oil pump.

The amount of lubricating oil supply required to lubricate the bearing of the rotor, which is a compression rotor, can be defined by a constant according to the specifications of the bearing, a bearing target temperature, and a load according to the rotation speed, the discharge pressure, and the gear. During operation of the compressor, the rotation speed or the discharge pressure acts as a variable, and the oil supply amount is varied according to either one of the two.

One example of such technology is described in Patent Literature 1, in which means for supplying oil to a bearing is controlled during no-load operation or low-speed rotation so as to reduce the oil supply amount compared with during load operation and to thereby reduce power consumption.

On the other hand, the relation between the pressure of compressed gas and the amount of gas discharged in a compressor can be designed variously according to the specifications. For example, an operation method of increasing the amount of gas at the same pressure is known (Patent Literature 2). An increase in amount of the gas discharged is controlled through rotation speed (the rotation speed of compression means, such as a screw, the rotation speed of a generator driving the compression means, etc.). Such an operation in which the discharge pressure is reduced while the rotation speed is increased is known as a low-pressure high-flow operation.

CITATION LIST Patent Literature

-   PATENT LITERATURE 1: JP-A-2002-364568 -   PATENT LITERATURE 2: JP-A-H9-209949

SUMMARY OF INVENTION Technical Problem

The amount of lubricating oil supply required for the bearing supporting the rotor of the compressor main body shall be defined by the following MATH. 1.

[MATH. 1]

Q=a×F×n  (MATH.1)

where Q is a required supply amount (1), F is a bearing load (N), n is a bearing rotation speed (min−1), and a is a coefficient.

Thus, in the case of the low-pressure high-flow operation, for example, determining the amount of oil to be supplied to the bearing according to either the discharge pressure (bearing load) or the rotation speed (bearing rotation speed) may result in an excessive oil supply. An excessive oil supply to the rotor bearing may reduce the efficiency of electric power consumption due to agitation loss etc. Moreover, there is also a risk of damage to the bearing etc.

In other words, according to Patent Literature 1, the amount of oil supplied to the bearing is reduced during no-load operation or low-speed rotation by means of one of the rotation speed and the discharge pressure (bearing load). However, in the case of an operation where the discharge pressure and the rotation speed are inversely related to each other, for example, the amount of oil supplied to the bearing cannot be controlled properly. It is desired that the amount of oil supplied to the bearing be properly controlled depending on various specifications of the discharge pressure (bearing load) and the rotation speed.

Solution to Problem

To solve the above problem, for example, the configuration described in the claims is adopted. Specifically, in one example, a gas compressor includes: a compressor main body having a rotor that compresses gas; a bearing that supports the rotor on a compressor main body casing; an oil case in which lubricating oil to be supplied to the bearing is stored; a lubricating oil pipe through which lubricating oil flows from the oil case to the bearing; an oil pump that pumps lubricating oil from the oil case to the bearing through the lubricating oil pipe; flow amount control means for adjusting an amount of lubricating oil flowing through the lubricating oil pipe; an electric motor that supplies power to the rotor; an inverter that outputs a rotation frequency of the electric motor; a pressure sensor that detects a discharge pressure of the compressor main body; and a control unit that determines an amount of lubricating oil to be supplied to the bearing from a load on the bearing corresponding to the pressure detected by the pressure sensor and a rotation speed of the rotor corresponding to the rotation frequency output by the inverter, and controls the flow amount control means on the basis of the amount of lubricating oil to be supplied.

Advantageous Effects of Invention

According to the present invention, a proper amount of lubricating oil can be supplied to the bearing according to the bearing load, depending on the discharge pressure, and the bearing rotation speed. The following description will reveal other objects, configurations, and effects of the present invention.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic view showing the overall general configuration of an oil-free compressor that is one embodiment employing the present invention.

FIG. 2 is a schematic view showing a processing relation in a control system of the embodiment.

FIG. 3 is a view illustrating a ratio of an amount of oil supplied to a bearing of the embodiment.

DESCRIPTION OF EMBODIMENTS

In the following, an embodiment of the present invention will be described using the drawings.

FIG. 1 illustrates the overall configuration of an oil-free screw compressor 100 (hereinafter may also be referred to simply as a compressor 100) that is one embodiment employing the present invention. In this example, the compressor 100 compresses air (atmospheric air). However, the compressor 100 is not limited to an oil-free screw compressor.

The compressor 100 mainly includes: a compressor main body 1 having a pair of male and female screw rotors (rotors) that can rotate in a non-contact, oil-free state by means of a timing gear, a compressed air heat exchanger 14 b that cools compressed air discharged from the compressor main body 1; lubricating oil 12 for a compressor bearing 16 and a gear used in driving units on the inside and outside (the suction side and the discharge side) of the compressor main body 1; a lubricating oil heat exchanger 14 c that cools the lubricating oil 12; a main body cooling oil heat exchanger 14 a that cools cooling lubricating oil for cooling the inside of a casing of the compressor main body 1; a gear case 11 (storage part) containing an oil case in which the cooling lubricating oil and the lubricating oil 12 are retained; an oil pump 10 that pumps oil from the gear case 11 to the bearing 16 of the screw rotors and gears 7, 8; and a control device A that controls operation of the compressor 100. The control device A is a programmable computer, and one feature of the control device A is controlling the amount of oil supplied to the compressor bearing 16 through the discharge pressure (bearing load) and the rotation speed.

A scavenge port 40 through which air inside a housing of the compressor 100 is removed is provided in an upper surface of the housing, and a suction port 41 through which outside air is suctioned is provided in a side surface of the housing facing a motor 2 that is located on the upstream side in an air flow inside the housing. Inside the housing near the scavenge port 40, a cooling fan 20 for scavenging is provided, and from the suction port 41 outside air flows roughly in the order of the motor 2, the compressor main body 1, and the heat exchangers 14 a, 14 b, and the outside air having reached an exhaust duct 35 is removed through the scavenge port 40 to the outside of the housing. The rotation speed of the cooling fan 20 is controlled by the control device A, such that the temperature inside the housing is maintained within a certain range, according to detection signals from various sensors (not shown) that monitor the pressure of compressed air, the temperature of the motor 2, etc.

The motor 2 can rotate at variable speeds by receiving electric power of an arbitrary frequency from an inverter 19 via the control device A. A driving pulley 3 a is installed at the end of the output shaft of the motor 2, and an output of the motor 2 is transmitted to a driving pulley 3 b through a driving belt 4 that is suspended on the driving pulley 3 a. The driving pulley 3 b is coaxially connected to the gear shaft 6. The gear shaft 6 is connected to the bull gear 7 disposed inside the gear case 11, and as the bull gear 7 meshes with the pinion gear 8 installed at an end of the male (or female) rotor shaft of the compressor main body 1, the power from the motor 2 is transmitted to the screw rotor.

The compressor main body 1 suctions outside air from a suction part through an air filter 5 and compresses the outside air. The compressed air is discharged to a pipe 25 a. The pipe 25 a is connected to the compressed air heat exchanger 14 b, but before that an air release path 26 is branched from the pipe 25 a. As an air release valve 27 provided on the downstream side of the air release path 26 opens and closes, the compressed air can be released into the atmosphere through the air release path 26. That is, when the consumption of compressor air on a user's side decreases and the pressure of the compressed air reaches a predetermined value, the compressor 100 performs no-load operation in which the load on the compressor main body 1 is reduced and thereby electric power consumption is reduced. During normal operation, the compressed air discharged to the pipe 25 a flows to the compressed air heat exchanger 14 b.

The compressed air heat exchanger 14 b is a tube-type or plate-type heat exchanger. The compressed air heat exchanger 14 b is supplied with a cooling fluid (water or coolant) (not shown) and cools the compressed air to a desired temperature through heat exchange with the cooling fluid before discharging the compressed air to the user's side through a pipe 25 b.

On the downstream side of the pipe 25 b, a pressure sensor 18 that measures a discharge pressure value and outputs the value to the control device A is installed. In other words, the pressure sensor 18 measures the pressure value on the side where the compressed air is used (user's side).

Next, a system for circulating the lubricating oil 12 will be described.

As in the rotation mechanism of the compressor main body 1, an oil pump driving gear 9 is installed at the shaft end of the gear shaft 6 on the opposite side from the pulley 3 b. The pump driving gear 9 meshes with a driven gear connected to the oil pump 10 and transmits power from the motor 2 to the oil pump 10. The oil pump 10 pumps the lubricating oil 12 stored in the gear case 11 to the lubricating oil heat exchanger 14 c through a lubricating oil pipe 13 a. The lubricating oil 12 having been cooled to or below a predetermined temperature in the lubricating oil heat exchanger 14 c is sent to the compressor bearing 16 on the discharge side and the suction side through a lubricating oil pipe 13 b and an oil filter 15, and is then recovered into the gear case 11.

The oil pump 10 uses the driving system of the compressor main body 1 through the pump driving gear 9 etc. Accordingly, the lubricating oil supply amount also increases and decreases as the rotation speed of the motor 2 increases and decreases. In this embodiment, the oil pump 10 is designed such that a required supply amount Q of the lubricating oil supplied from the oil pump 10 according to the rotation speed satisfies the following (MATH. 1) during normal operation (so-called rated operation).

[MATH. 1]

Q=a×F×n  (MATH.1)

where Q is a required supply amount (1), F is a bearing load (N), n is a bearing rotation speed (min−1), and a is a coefficient.

Between the secondary side of the oil pump 10, which is the upstream side of the lubricating oil pipe 13 a, and the gear case 11, an oil drain solenoid valve 17 and a lubricating oil pipe 13 c are provided as flow amount control means for controlling the supply of lubricating oil. As the oil drain solenoid valve 17 is opened (turned on) according to a command from the control device A, the lubricating oil 12 delivered from the pump 10 returns to the gear case 11 through the lubricating oil pipe 13 a. Thus, it is possible to control the amount of lubricating oil flowing through the lubricating oil pipes 13 a, 13 b by opening and closing (turning on and off) the oil drain solenoid valve 17, and as a result, the amount of oil supplied to the bearing 16 is increased and reduced. This is because, during a low-pressure high-flow operation to be described later, it is necessary to restrict the amount of lubricating oil supplied.

The oil drain solenoid valve 17 is so configured that, when the valve is opened (turned on), the lubricating oil is not entirely returned to the gear case 11 through the lubricating oil pipe 13 c but only a part of the lubricating oil is returned while the rest is pumped to the lubricating oil pipe 13 a etc. The amount of lubricating oil pumped to the lubricating oil pipe 13 a upon opening (turning on) of the oil drain solenoid valve 17 is equivalent to the required supply amount (Q) that is a proper amount according to the bearing load and the bearing rotation speed. The required supply amount (Q) will be described later.

The means for controlling the amount of lubricating oil 12 supplied is not limited to the oil drain solenoid valve 17. For example, the pump 10 may employ an autonomous generator (motor etc.) and the degree of driving may be controlled according to a command value from the control device A etc., or these valve and generator may be used in combination. In this embodiment, the oil drain solenoid valve 17 will be described as being switched between two stages of open and closed, but this is not limitative and the number of stages can be more than two.

Next, the control system of the control device A is schematically shown in FIG. 2. The control device A is a programmable computer including an arithmetic unit and a volatile or nonvolatile memory, and software and the arithmetic unit work together to input and output control signals between units of the compressor 100 and the control device A. The control device A receives inputs of a set pressure value input by an operator from an input panel (not shown) installed on the outer periphery of the housing etc., or from a control apparatus (including a PC and a server) outside the compressor 100 through a network, and stores the inputs in the memory (not shown).

The control device A receives the current pressure value output from the pressure sensor 18 in real time or at predetermined intervals, and compares the current pressure value with the set pressure value stored in the memory. Until the current pressure value reaches the set pressure value, the control device A gives a command on a predetermined rotation frequency to the inverter 19 so as to operate the compressor main body 1 under loaded conditions. Then, the control device A receives a feedback on the current frequency value from the inverter 19.

On the other hand, when the current pressure value from the pressure sensor 18 reaches the set pressure value, the control device A switches to the control of no-load operation. During no-load operation, the control device A opens the air release valve 27 to release air via a released air silencer, and outputs a command to reduce the rotation frequency to the inverter 19 in order to reduce the rotation speed of the compressor main body rotor. Thereafter, the control device A continuously monitors the current pressure value from the pressure sensor 18, and when the pressure value has decreased to or below the set pressure or to near the set pressure according to the consumption of compressor air on the user's side, the control device A resumes load operation by closing the air release valve 27 and giving a command to increase the rotation frequency to the inverter 19 until the set pressure value is reached.

The control device A determines whether to open or close the oil drain solenoid valve 17 by comparing, with a prescribed value, the pressure detected by the pressure sensor 18 and the result of an output frequency command value of the motor 2 obtained on the basis of the detected pressure. The low-pressure high-flow operation of the compressor 100 will be described first, and then the control of the oil drain solenoid valve 17 will be described.

In this embodiment, the compressor 100 is configured to be able to perform the low-pressure high-flow operation. Here, the low-pressure high-flow operation refers to an operation in which the rotation speed of the compressor rotor is increased relative to the discharge pressure of the compressor main body 1 to increase the amount of air relative to the discharge pressure. The rotation speed of the compressor rotor is increased within the same range as power consumption during normal operation. Thus, it is possible to generate low-pressure compressed air in a larger amount with constant power consumption.

The control of such operation is performed by changing the output frequency of the inverter 19. For example, during normal operation (rated operation), the control device A makes the inverter 19 drive the motor 2 at a preset frequency corresponding to a set pressure value. If the frequency at this point is regarded as a rated frequency, the motor 2 is driven at a frequency higher than the rated value during the low-pressure high-flow operation.

The operation state of the low-pressure high-flow operation may be changed by an operator inputting and setting the pressure and the flow through the above-mentioned input panel etc., or the pressure and the frequency value may be stored in advance in the memory as default values for the low-pressure high-flow operation, and the operator may switch the operation mode from the input panel. In this embodiment, the operation in which the pressure is lower and the frequency is higher than those in the rated operation will be described as the low-pressure high-flow operation, but the present invention is applicable regardless of the frequency of whichever operation is regarded as a rated frequency.

When the relation between the discharge pressure (bearing load) and the rotation speed of the rotor is not the same as between the rated operation and the low-pressure high-flow operation, the amount of lubricating oil to be supplied to the bearing 16 also needs to be changed according to the operation conditions. That is, if the amount of lubricating oil to be supplied during the low-pressure high-flow operation is the same as during the rated operation, the supply amount becomes excessive, resulting in mechanical loss.

FIG. 3 shows a relation between the rotation frequency ratio and the bearing oil supply amount ratio, and the operation of the oil drain solenoid valve 17. In FIG. 3, the line C represents the amount of oil supplied to the bearing relative to the rotation frequency ratio. It is assumed here that the required amount of oil supplied to the bearing 16 is, for example, calculated by (MATH. 1) described above.

According to (MATH. 1), even if the rotation frequency increases, if the load on the bearing 16 decreases (the compression pressure in the working chamber decreases), the required amount of oil supplied to the bearing 16 remains the same. For example, in the low-pressure high-flow operation, when the rotation frequency ratio reaches 120%, the load reaches 80%, which means that the required supply amount can be equivalent to that at the rotation frequency ratio of 100%.

By contrast, in the conventional method of determining an increase in amount of oil to be supplied to the bearing according to an increase in the rotation frequency, an area D in the high-speed rotation region represents a state of an excessive oil supply relative to the required supply amount.

The power consumption of the compressor 100 includes mechanical loss incurred in the compressor bearing 16, and the mechanical loss mainly includes loss that varies with the rotation speed and friction loss that varies with the oil supply temperature and the oil supply amount. Under low-pressure high-flow conditions when the rotation frequency ratio is above 100%, the control device A opens the oil drain solenoid valve 17 to reduce the amount of oil supplied to the bearing 16. Thus, the power consumption due to friction loss etc. can be reduced (e.g., about one to several percent reduction, which varies depending on the specifications).

Specifically, the control device A obtains the required supply amount (Q) from the bearing load (F) corresponding to the current pressure value from the pressure sensor 18, the bearing rotation speed (n) corresponding to the output frequency value fed back from the inverter 19, and the coefficient (a), and determines whether or not the amount of oil pumped by the oil pump 10 corresponding to the output frequency value is above the required supply amount (Q) obtained. If the former amount is larger, the control device A gives a command to open (turn on) the oil drain solenoid valve 17 to restrict the amount of lubricating oil pumped to the lubricating oil pipes 13 a, 13 b. Thereafter, too, the control device A monitors the required supply amount and the current pumping amount of the oil pump 10 on the basis of the corresponding bearing load and the corresponding bearing rotation speed obtained from the current pressure value from the pressure sensor 18 and the output frequency fed back from the inverter 19, and controls opening and closing (turning on and off) of the oil drain solenoid valve 17. In this way, the control device A controls the proper amount of oil supplied to the bearing 16 according to the bearing load and the bearing rotation speed.

Thus, according to the compressor 100, it is possible to obtain an optimal amount of lubricating oil 12 to be supplied according to the relation between the rotation frequency and the discharge pressure, and to further reduce the power consumption by reducing unnecessary loss.

In the compressor 100, even when the oil drain solenoid valve 17 is in the open state, a certain amount of lubricating oil is pumped to the lubricating oil pipe 13 a, so that it is unlikely that the supply of lubricating oil to the bearing 16 etc. stops while the compressor main body 1 is being driven.

In the compressor 100, the lubricating oil pipe 13 c and the oil drain solenoid valve 17 are provided to adjust the amount of lubricating oil supplied to the bearing 16 etc. Thus, it is possible to adjust the amount of lubricating oil while securing the configurational advantage that the driving system of the compressor main body is used as the driving system of the oil pump for higher efficiency of the configuration.

While the embodiment of the present invention has been described above, it goes without saying that the present invention is not limited to the above configuration but embraces various changes and equivalents within the scope of the invention.

In this embodiment, the example has been described in which the control device calculates the proper amount of lubricating oil according to the bearing load and the bearing rotation speed corresponding to each of the current pressure sensor value, the input set pressure value, and the frequency command value for the inverter 19. Alternatively, a correspondence table of a calculated amount of oil to be supplied associated with the pressure and the frequency may be stored in advance in the memory, and whether to open or close the oil drain solenoid valve 17 may be determined on the basis of this correspondence table. Thus, the burden of the calculation process can be relieved.

Such a correspondence table may be stored for each of the normal operation and the low-pressure high-flow operation, and the correspondence table may be switched along with the operation mode. Moreover, the table may be used during one of the normal operation and the low-pressure high-flow operation while calculation may be performed in the control device A during the other operation, or vice versa.

In this embodiment, the example has been described in which the driving system of the compressor main body 1 is also used as the driving system of the oil pump 10, but the oil pump 10 may use an independent driving system with a small electric motor, and a driving command may be output from the control device A to the oil pump 10 so as to adjust the amount of lubricating oil to be supplied. Specifically, when the required supply amount (Q) of lubricating oil obtained by the control device A is larger than the current amount supplied by the oil pump 10, the control device A outputs a command to reduce the rotation speed of the small electric motor, and when the required supply amount (Q) is smaller than the current supply amount, the control device A outputs a command to increase the rotation speed of the small electric motor.

In this embodiment, a single-stage compressor has been taken as an example of the compressor 100, but the compressor 100 may be a multi-stage compressor composed of a low pressure-stage compressor and a high pressure-stage compressor. Moreover, the compression means is not limited to the pair of male and female screw compressor main bodies, but any compression means of which the bearing is supplied with lubricating oil can be employed (e.g., scroll compressors, claw compressors, and single- or triple-screw compressors).

In this embodiment, the double-rotor screw compressor has been described as to the rotor of the compressor. However, the rotor may be a single rotor or triple rotors, and the present invention is applicable to the control of the bearing oil supply amount in compressors, such as scroll compressors, reciprocating compressors, claw compressors, and compressors combining a screw and a rotating compression plate.

REFERENCE SIGNS LIST

-   1 Compressor main body -   2 Motor -   3 a, 3 b Pulley -   4 Belt -   5 Air filter -   6 Gear shaft -   7 Bull gear -   8 Pinion gear -   9 Oil pump driving gear -   10 Oil pump -   11 Gear case -   12 Lubricating oil -   13 a, 13 b, 13 c Lubricating oil pipe -   14 a Main body cooling fluid heat exchanger -   14 b Compressed air heat exchanger -   15 Oil filter -   16 Compressor bearing -   17 Oil drain solenoid valve -   18 Pressure sensor -   19 Inverter -   20 Cooling fan -   25 a Compressed air pipe -   26 Air release path -   27 Air release valve -   28 Released air silencer -   29 Check valve -   30 Two-way solenoid valve -   35 Air duct -   A Control device 

1. A gas compressor comprising: a compressor main body having a rotor configured to compress gas; a bearing configured to support the rotor on a compressor main body casing; a storage part in which lubricating oil to be supplied to the bearing is stored; a lubricating oil pipe through which lubricating oil flows from an oil case to the bearing; an oil pump configured to pump lubricating oil from the oil case to the bearing through the lubricating oil pipe; flow amount control means configured to adjust an amount of lubricating oil flowing through the lubricating oil pipe; an electric motor configured to supply power to the rotor; an inverter configured to output a rotation frequency of the electric motor; a pressure sensor configured to detect a discharge pressure of the compressor main body; and a control unit configured to determine an amount of lubricating oil to be supplied to the bearing from a load on the bearing corresponding to the pressure detected by the pressure sensor and a rotation speed of the rotor corresponding to the rotation frequency output by the inverter, and control the flow amount control means on the basis of the amount of lubricating oil to be supplied.
 2. The gas compressor according to claim 1, further comprising an oil drain pipe through which lubricating oil returns from the lubricating oil pipe to the storage part, wherein the flow amount control means is a two-way solenoid valve, and the two-way solenoid valve is disposed on the oil drain pipe.
 3. The gas compressor according to claim 2, wherein the flow amount control means is driven by power from the electric motor.
 4. The gas compressor according to claim 1, wherein the flow amount control means is driven by another electric motor different from the electric motor.
 5. The gas compressor according to claim 1, wherein the control unit stores in advance a correspondence table of the amount of lubricating oil to be supplied to the bearing associated with the load on the bearing corresponding to a pressure of compressed gas discharged by the compressor main body and the rotation speed of the bearing corresponding to the rotation frequency output by the inverter, and with reference to the correspondence table, the control unit controls the flow amount control means on the basis of the amount of lubricating oil corresponding to an input value of at least one of the pressure detected by the pressure sensor and the rotation frequency output by the inverter.
 6. The gas compressor according to claim 1, wherein the control unit controls a low-pressure high-flow operation in which a rotation speed of the electric motor is increased with the same power consumption of the electric motor as when discharged gas of a specific pressure and a specific flow is produced, and discharged gas of a pressure lower than the specific pressure and a flow higher than the specific flow is discharged by the compressor main body.
 7. The gas compressor according to claim 6, wherein the control unit controls the flow amount control means during the low-pressure high-flow operation. 